Much of the power of the retina to process and package information is derived from the properties of retinal synapses. It is known, from anatomical studies, that retinal synapses have structural features suggesting they work differently from more familiar synapses elsewhere in the nervous system. Presently though, the physiology of retinal synapses is very imperfectly understood. This proposal describes electrophysiological experiments to investigate the normal working of retinal synapses, concentrating in particular, on the first synapse of the visual system: the synapse between photoreceptors and bipolar cells. Four sets of questions are addressed here, each of which is a continuation of our present work. A first set of questions concerns the properties of channels, on bipolar cells, that are opened by the photoreceptor transmitter, glutamate. We have recently discovered that these channels have some unorthodox and surprising properties that we intend to examine in more detail. A second set of questions is concerned with the presynaptic mechanisms involved in the release of transmitter from photoreceptors. To tackle these questions we have developed the sparse culture of chick retinal cells as a preparation that avoids the technical problems associated with the intact retina. The third group of questions centers on the role of the peptide, somatostatin, in the outer retina. This peptide, which in the amphibian retina is probably the neurotransmitter of an interplexiform cell, has been shown to have diverse, modulatory actions in other parts of the nervous system. We propose to describe somatostatin's effects in the intact retina and uncover the underlying mechanisms by examining isolated retinal neurons. Lastly, we want to find out more about two important membrane currents found in chick cone cells. One of these currents is the calcium current involved in transmitter release.